Twice-Functionalized Montmorillonite Nanosheets for Polymer-Derived MMT-SiOC Nanocomposites: Phase Formation and Porosity.

In this study, montmorillonite (MMT) nanosheets are purified and exfoliated from a crude clay source and further twice-functionalized with cetritrimethylammonium bromide and [3-(2-aminoethylamino)propyl]trimethoxysliane (AEAPTMS) to promote dispersion in the preceramic polymer. Phase profiles and compositions of MMT nanoflakes and MMT-silicon oxycarbide (SiOC) are characterized with X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The microstructures are examined by scanning and transmission electron microscopy. MMT nanoflakes are randomly dispersed in the SiOC matrix with α-quartz forming at the MMT-SiOC interface. Pyrolysis to 1400 °C induced the formation of SiC nanowhiskers that are observed up to 20 µm in length and 200 nm in diameter. After selective etching of SiO(2) domains with HF, pore sizes and specific surface areas of MMT-SiOC are analyzed with nitrogen adsorption. The study provided a new fundamental understanding of MMT-SiOC interactions at different pyrolysis temperatures and also led to composites with specific surface areas reaching 120 m(2) g(-1) up to 1200 °C pyrolysis, and between 340 and 772 m(2) g(-1) at 1400 °C pyrolysis and pore size distributions between 2 and 5 nm. The methodology and results presented improve the understanding and viability of 2D nanomaterial-reinforced ceramic composites and MMT as a precursor for nanostructured SiC.